1. Field of the Invention
The present invention relates to a laser processing apparatus which performs processing by radiating a laser beam from a laser beam generator to the surface of a workpiece. More particularly, the present invention relates to a laser processing apparatus capable of performing different kinds of processings under different conditions in an optimum and efficient manner using only a single processing apparatus.
2. Description of the Related Art
Heretofore, laser processing apparatuses of this type have performed thermal processings such as cutting and welding by radiating a laser beam to the surface of a workpiece. As an example, reference is made hereby to the apparatus shown in FIG. 6. First, the construction of this conventional laser processing apparatus will be described below.
This conventional laser processing apparatus generally comprises a laser beam generator 51, a reflecting mirror 53, a processing head 54, a condenser lens 55 and a processing nozzle 56.
The laser beam generator 51 emits a laser beam 52 of 10.6 .mu.m (micrometer) wavelength, the construction of the laser beam generator 51 being generally known well, so the details thereof will be omitted here.
The reflecting mirror 53 changes the travelling direction of the laser beam 52 emitted from the laser beam generator 51. In general, the reflecting mirror 53 is made of copper, and the surface thereof is plated with gold.
The processing head 54 has a generally cylindrical, hollow shape and is constituted by a metal such as aluminum or iron.
The condenser lens 55, having a focal length F, is fixedly disposed in the interior of the processing head 54, and the laser beam 52 reflected by the reflecting mirror 53 is incident on the condenser lens 55. The laser beam 52 thus incident on the condenser lens 55 passes through the condenser lens while being converged by the same lens, and a focal point 58 is formed at a focal length F below the condenser lens 55. In the position of the focal point 58, there is disposed a workpiece 61 which will be described later. The condenser lens 55 is constituted of, for example, zinc selenide (ZnSe), potassium chloride (KCl), or gallium-arsenic (GaAs).
The processing nozzle 56, made of copper, is removably mounted to a front end portion of the processing head 54. The nozzle 56 has a generally conical shape and the interior thereof is tapered and hollow. An ejection opening 57 is provided at a tip end of the nozzle. The laser beam 52 which has been converged by the condenser lens 55 passes through the ejection opening 57 and forms the focal point 58 on the workpiece 61. A processing gas supply port 59 is provided in a part of a side face of the nozzle 56. Processing gas 60 fed through the processing gas supply port 59 is jetted from the ejection opening 57 of the nozzle 56.
The operation of the conventional laser processing apparatus having the above construction will be described below.
The travelling direction of the laser beam 52 emitted from the laser beam generator 51 is changed by the reflecting mirror 53. The laser beam 52 is then incident on the condenser lens 55 in the processing head 54. The laser beam 52 is converged by the condenser lens 55, passes through the ejection opening 57 of the nozzle 56, and is then jetted to the exterior of the nozzle. The laser beam 52 from the processing nozzle 56 forms the focal point 58 at a focal length F under the condenser lens 55. The processing gas 60 fed from the processing gas supply port 59 is also jetted from the ejection opening 57 of the nozzle 56.
The workpiece 61 is disposed in the position of the focal point 58 or thereabouts such that the workpiece 61 is fixed to a moving device 62. The moving device 62 is moved while the laser beam 52 is radiated onto the workpiece 61, whereby a spot of the laser beam formed on the workpiece 61 moves in a relative manner. In this way, a predetermined thermal processing is applied to the workpiece 61 using the laser beam 52.
As examples of such thermal processing, cutting and welding work will be explained below. FIG. 7 is a partially enlarged sectional view of the processing nozzle 56 in cutting work, and FIG. 8 is a partially enlarged sectional view of the processing nozzle 56 in welding work.
In cutting work, as shown in FIG. 7, the laser beam 52 is radiated to the workpiece 61, and at the same time the processing gas 60 which is active gas, e.g., oxygen gas, is forcefully directed to the workpiece 61 through the ejection opening 57. As a result, the portion of the workpiece 61 melted as molten metal 63 by the laser beam 52 is blown off by the strong stream of the processing gas 60, to form a cut slot 64 in the workpiece 61. In this case, in order to strengthen the stream of the processing gas 60, the ejection opening 57 formed at the nose of the processing nozzle is relatively small, and the distance between the ejection opening 57 and the workpiece 61 is relatively short.
On the other hand, in welding work, as shown in FIG. 8, the laser beam 52 is radiated to the workpiece 61, and at the same time the processing gas 60 which is inert gas, e.g., argon gas, is weakly applied to the workpiece 61 through the ejection opening 57. As a result, the portion of the workpiece 61 melted as molten metal 63 by the laser beam 52 is covered with a weak stream of the processing gas 60, and again solidifies while the oxidation thereof is prevented. In this way, a welded portion 65 is formed in the workpiece 61. In this welding work, even if the processing nozzle 56 used in the foregoing cutting work is used as it is, it is possible to change the kind and flow rate of processing gas 60, but the nose portion of the nozzle 56 may be melted by a high-temperature plasma 66 generated in the welded portion. Therefore, in the case of the processing nozzle 56 used for welding work, it is desirable that the distance between the ejection opening 57 and the workpiece 61 be longer than that in the cutting work. In the case of a longer distance between the ejection opening 57 and the workpiece 61, the diameter of the laser beam 52 jetted from the ejection opening 57 also becomes larger. For this reason, the diameter of the ejection opening 57 of the processing nozzle 56 for welding work is set larger than that of the ejection opening 57 of the processing nozzle 56 for cutting work.
Thus, it is desirable to use a processing nozzle 56 having a shape in accordance with the kind of a thermal processing to be performed. Also, in the case where processings of the same type are to be performed, it is desirable to select optimum nozzle shapes according to processing conditions adopted.
In the case of performing different types of thermal processings in such a conventional laser processing apparatus as described above, it is necessary to change processing nozzles from one to another appropriately according to the type of the thermal processing to be done. In the conventional laser processing apparatus, this nozzle changing operation is conducted manually, thus causing the problem of deterioration of production efficiency.
As another conventional example, as shown in FIG. 9, a laser processing apparatus has been proposed which is provided with each of plurality of processing heads 67, condenser lenses 68 and processing nozzles 69 (three in this conventional example) according to processings required. According to the construction of this conventional laser processing equipment, the laser beam 52 from the laser beam generator 51 is conducted to the required processing nozzle 69 by changing the position of a reflecting mirror 70 to the position corresponding to the required processing nozzle 69. With this construction, the deterioration of production efficiency is avoidable because it is not necessary to perform the removal and replacement of the processing nozzle 69 with respect to the processing head. However, since it is necessary to provide the same number of condenser lenses 68, which are expensive, as the number of the processing nozzles 69 used. Accordingly, an increase in cost results, and since the number of the processing heads 67 must also be the same as the number of the processing nozzles 69, the size of the entire laser processing apparatus also becomes very large.